In the context of the transmission of TM modes and/or TM waves, only the electrical field has a component in the direction of propagation, and the magnetic fields are entirely perpendicular to the direction of propagation. TM waves are therefore also called E waves. A multiplex filter in this context comprises a common connection and at least two signal line connections, wherein the at least two signal line connections are each connected to the common connection via one signal transmission path. The direction of signal transmission can be from the common connection to one of the multiple signal line connections (for example in the form of a diplexer or multiplexer), and also simultaneously from another one of the signal line connections to the common connection (for example in the form of a duplexer which has two further connections in addition to the first common connection). Each signal transmission path passes through different resonator chambers such that different frequency ranges are filtered in the same.
The publication by M. Höft and T. Magath, “Compact Base-Station Filters Using TM-Mode Dielectric Resonators,” describes the construction of a high-frequency filter which has multiple dielectric resonators. In this case, the individual resonators are coupled parallel to the direction of propagation of the H field.
A disadvantage of this construction is that more space is required to implement the desired filter properties. This space requirement increases in proportion to the number of signal transmission paths which should be included.
Therefore, the problem addressed herein is that of creating a multiplex filter which is particularly suitable for the transmission of TM modes in the transverse direction, wherein this multiplex filter should be constructed in both a space-saving and cost-effective manner.
This problem is addressed with respect to a multiplex filter and a method for tuning such a multiplex filter. Advantageous non-limiting implementations of the multiplex filter or of the method for tuning the multiplex filter are provided.
The multiplex filter has a housing which has a housing base, a housing cover spaced apart from the housing base, and a circumferential housing wall between the housing base and the housing cover. The housing base and the housing cover are preferably intersected by a central axis. The multiplex filter also has at least n filter chambers which are surrounded by the housing and/or at least one insert positioned in the housing.
A dividing device which consists of metal or which comprises metal is constructed in each of the n filter chambers, dividing each filter chamber into m resonator chambers, wherein m≥2, and wherein each of the same form one resonator. The dividing devices are arranged parallel to the central axis or with a component substantially parallel to the central axis and divide the filter chamber into m resonator chambers parallel to the central axis or with a component substantially parallel to the central axis. The resonator chambers in each filter chamber, and therefore each of the resonators, are decoupled from each other by the dividing devices situated in each filter chamber. In addition, at least n dielectrics are included, of which at least one is arranged in each filter chamber. The multiplex filter has n−1 separators. The n filter chambers are arranged along a central axis which is perpendicular to the H field, or with a component essentially perpendicular to the H field, wherein every two filter chambers which are adjacent or are adjacent along the central axis are separated by one separator. Each of the n−1 separators has at least m coupling openings via which every two resonator chambers which are adjacent in the signal transmission direction are coupled to each other. The resonator chambers are coupled perpendicular to the H fields and/or parallel to the central axis or with a component essentially perpendicular to the H fields and/or parallel to the central axis. A common connection is guided into the first filter chamber via a first opening in the housing, and is coupled in the same to the m resonators of the m resonator chambers. As a result of the fact that the coupling is established perpendicular to the H field, the resonator can have a very compact construction. In addition, m signal line connections are coupled via m openings in the housing to the m resonators in the m resonator chambers in the nth filter chamber.
It is particularly advantageous in this case that the individual filter chambers, and accordingly the individual resonator chambers with the resonators are stacked one above the other, wherein the same are coupled by coupling openings which are constructed inside the separators. The coupling is in the signal transmission direction, and therefore perpendicular to the H field. This enables a very compact construction of the resonator because multiple signal transmission directions are established parallel to the central axis and are uncoupled from each other.
The method for tuning the multiplex filter comprises various method steps. In one method step, at the beginning, all coupling openings of the 1+Xth separator and/or the n−1−Xth separator are closed, wherein X is equal to 0 at the beginning. In a further method step, a reflection parameter is measured at the common connection and/or at least one, and preferably all, signal line connections. Subsequently, the resonance frequency and/or the coupling bandwidth, and/or the input coupling bandwidth, is/are adjusted to a desired value. This method can be used to adjust the resonance frequency and/or the coupling bandwidth of m resonator chambers of a filter chamber to the desired value independently of further resonator chambers in other filter chambers.
There is a further advantage when one or both end faces of each of the n dielectrics are coated with a metal layer, wherein this metal layer then constitutes one of the n−1 separators, and wherein at least one recess inside the metal layer forms the at least one coupling opening. The use of accordingly coated dielectrics enables a further reduction of the size of the high-frequency filter.
There is also a further advantage for the multiplex filter if a diameter of at least one, and preferably all, filter chambers is defined and/or prespecified by at least one insert in each case, and particularly by an annular insert which leans against the housing wall. The resonance frequency can be tuned in this way. The configuration of the insert leaning against the housing wall in a form-fitting manner also ensures that the insert cannot slide from its position over time.
The insert of one, and preferably of each, filter chamber has wall segments adjacent to the inner wall of the housing with different thicknesses, such that it is possible to adjust the volumes of individual resonator chambers of a filter chamber independently of each other, and/or for said volumes to differ from each other. The use of such inserts further increases the flexibility of the multiplex filter.
A further advantage of the multiplex filter arises when the inserts of at least two of the n filter chambers which do not directly follow each other—that is, are not adjacent to each other—have an opening, and the at least two openings are connected to each other by a channel which runs, by way of example, at last partially inside the housing wall. An electrical line runs in this channel, and the electrical line couples the two resonator chambers of the different filter chambers to each other capacitively and/or inductively. In this way, despite the compact construction of the multiplex filter, it is possible to achieve an overcoupling of resonators which are not directly adjacent.
An advantage also arises when at least one anti-turning element is attached between at least one of the n−1 separators and the at least one insert and/or the adjacent dielectric, to prevent these elements from turning with respect to each other. In this case, it is possible for at least one anti-turning element to be attached in each case between the housing base and/or the housing cover and/or the housing wall and the insert in the first filter chamber and the nth filter chamber, the same preventing these elements from turning with respect to each other. This ensures that the resonance frequencies and the group delays of the individual resonators do not change over time due to vibration in the high-frequency filter.
The n dielectrics inside the multiplex filter can have a disk shape, and/or all or some of the n dielectrics can have completely or partially differing dimensions. It is also possible for all or at least one of the n dielectrics to fully or partially fill in the volume of their respective filter chambers, and therefore of the m resonator chambers. The behavior of each resonator with respect to its resonance frequency and its coupling bandwidth can be accordingly adjusted by the geometric form and the arrangement of the dielectrics.
The dividing device is preferably formed by a plurality of through-connections inside the dielectric, which are arranged in the filter chamber parallel, or at least with one component parallel, to the central axis, thereby dividing the dielectric into m parts, wherein each of the m parts is found in one of the m resonator chambers of a filter chamber. This enables the use of a single dielectric, which is preferably made of a ceramic. In contrast, it would be possible for the dielectric to be composed inside each filter chamber of m parts which are preferably the same size, wherein each of the m parts is found in one of the m resonator chambers in a filter chamber, and wherein a metal layer is formed inside each filter chamber between the m parts as a dividing device. This metal layer separates the individual resonator chambers inside a filter chamber from each other, wherein the metal layer is arranged parallel to, or at least with one component parallel to, the central axis. A metal layer can be, by way of example, an electrically conductive coating on the lateral peripheral surface of the dielectric. Such an electrically conductive coating must be applied only at the locations of the m parts which are not in contact with the insert or with another already coated part of the m parts.
At least two or all of the n dielectrics, or two or all of the m parts of at least one dielectric, are made of a different material. In this case, it is also possible that at least one or all of the n dielectrics preferably have at least one recess filled with air. In this way, it is possible to separately change the resonance frequency for each resonator of a resonator chamber inside a filter chamber.
The first filter chamber has a region in which the dividing device only extends through the first dielectric over a sub-length of the diameter, thereby forming an opening region in which the common connection is coupled in the first filter plane to all m resonators, wherein the opening region has a size or length which is less than 10%, preferably less than 20%, more preferably less than 30%, more preferably less than 40%, and more preferably less than 50% of the smallest diameter of the first filter chamber. In this way, it is possible for a common connection to be used as a shared connector. By way of example, a mobile radio antenna can be connected to the common connection, wherein signals are transmitted via the same and signals are received by the same.
The signal transmission direction runs through each of the m signal line connections either from the signal line connection to the common connection or from the common connection to the signal line connection. If the signal transmission direction runs from one or more of the signal line connections to the common connection, one resonator of one resonator chamber of a filter chamber is coupled to precisely one resonator of one resonator chamber of a filter chamber which is adjacent in the signal transmission direction. This ensures that one resonator chamber is coupled to precisely one further resonator chamber along the route toward the common connection in the signal transmission direction. In the opposite direction, in the case in which the signal transmission direction runs from the common connection to one or more of the m signal line connections, one resonator of one resonator chamber of a filter chamber is coupled to one or more resonators of one filter chamber which is adjacent in the signal transmission direction. This means that in this case one resonator of one resonator chamber is coupled to more than one resonator of multiple resonator chambers of a further filter chamber. As such, it is possible to create additional signal transmission paths. However, this is preferably only true if the signal transmission direction runs from the common connection to the m signal line connections.
The coupling between the individual resonators is increased by the dielectric in the first resonator being in contact with the first separator, and the dielectric in the nth resonator being in contact with the n−1th separator, wherein the remaining dielectrics of the remaining n−2 resonators are in contact with both of the separators bounding the filter chamber in question. This is particularly advantageous if the dielectric in the first resonator is additionally in contact with the housing cover and the dielectric in the nth resonator is in contact with the housing base. The phrase “in contact” is used to indicate that two entities at least touch. The dielectrics of the n filter chambers in this case are preferably fixed to the respective separator or the respective separators, thereby improving the coupling.
In a further embodiment of the multiplex filter, the common connection contacts the dielectric in the first filter chamber either centrally or off-center. The dielectric in the first filter chamber has a depression into which the common connection projects, and as a result the common connection is in contact with the first dielectric, or the dielectric in the first filter chamber has a recess which passes through the same, through which the common connection extends such that the common connection is in contact with the first dielectric and is in contact with the first separator. The same is true for the m signal line connections. These have a central or off-center contact with the dielectric which is arranged in the m resonator chambers of the nth filter chamber. The dielectric in the nth filter chamber has up to m depressions into which the m signal line connections project, and as a result the m signal line connections are in contact with the nth dielectric, and/or the dielectric in the nth filter chamber has up to m recesses passing through the same, through which the m signal line connections extend such that the m signal line connections are in contact with the nth dielectric and are in contact with the n−1th separator.
A further advantage of the multiplex filter is a result of the fact that the arrangement and/or the size and/or cross-section shape of at least one coupling opening of one of the n−1 separators differs entirely or partially from the arrangement and/or the size and/or the cross-section shape of another coupling opening of the same n−1 separator or from a coupling opening of another of the n−1 separators. As an alternative or in addition thereto, the number of the coupling openings in the n−1 separators can be entirely or partially different among the same, and/or the number of the coupling openings of one of the n−1 separators used for the coupling of a resonator is different from the number of the coupling openings of the same separator used for the coupling of another resonator. This enables an adjustment of the coupling between the individual resonators to the desired value.
For further tuning of the high-frequency filter, it is also possible that at least one, and preferably all of the resonator chambers of at least one, and preferably all of the filter chambers have at least one additional opening toward the outside of the housing, wherein at least one tuning element can be inserted via this additional opening into the resonator chamber of at least one filter chamber. The distance between the tuning element which is inserted through the at least one additional opening into the at least one resonator chamber of at least one filter chamber can be modified for the corresponding, respective dielectric inside the at least one resonator chamber in the at least one filter chamber. In this case, multiple tuning elements can also be inserted into one resonator chamber, wherein one tuning element consists, by way of example, entirely of a metal or a metallic coating, whereas the other tuning element comprises a dielectric material. The tuning element which consists of a metallic material can be used for coarse tuning, and the tuning element which comprises a dielectric material can be used for fine tuning of the resonator frequency and/or the coupling bandwidth of the corresponding resonator.
In this case, the distance between the at least one spacer element and the respective dielectric inside the at least one of the m resonator chambers of the at least one of the n filter chambers can also be reduced to such an extent that it is in direct contact with the same. The dielectric of at least one of the n filter chambers can also have at least one indentation, wherein the distance between the tuning element and the dielectric can be reduced in such a manner that the tuning element dips into the indentation of the respective dielectric and is in contact with the same. The tuning element in this case enters into the at least one of the m resonator chambers of at least one of the n filter chambers particularly perpendicularly to the signal transmission direction—that is, preferably perpendicular to the central axis.
A method for tuning the multiplex filter is accordingly repeated for the remaining filter chambers. After the resonance frequency and/or the coupling bandwidth of at least one resonator, and preferably all resonators in the first and/or last—that is, nth—filter chamber have been adjusted to the desired value, in a further method stop at least one, and preferably m or more coupling openings of the 1+Xth separator and/or the n−1−Xth separator are opened. Then the value of the counter variable X is increased by 1. The previous method steps are then carried out once more. Once again, a reflection factor is measured on the common connection and/or a reflection factor is measured on at least one, and preferably on all m signal line connections. Subsequently, the coupling openings to the following resonators in the following filter chambers are opened and the value of the counter variable is once again increased. The tuning of the multiplex filter begins with the resonators into which the common connection and the m signal line connections engage—that is, with the resonators of the outermost filter chamber—and ends with the resonators which are arranged in the filter chamber (for an odd number n) or the filter chambers (for an even number n) in the center of the multiplex filter.
In the event that the multiplex filter has an uneven number of filter chambers, the filter chambers in the center of the multiplex filter must be utilized once for the measurement of the reflection factor on the common connection, and another time for the measurement of the reflection factor on at least one, and preferably all, of the m signal line connections. The coupling openings of the two separators which surround the filter chamber in the center of the multiplex filter must be closed to the other connector in each case—that is, to the common connection or to at least one, and preferably all, of the m signal line connections, according to the measurement of the respective reflection factor.
Subsequently, or if, for an even number of filter chambers, all coupling openings are open, the forward transmission factor and/or the reverse transmission factor can be measured, in addition to the reflection factors on the common connection and/or on at least one, and preferably all, of the m signal line connections.
The resonance frequencies and/or the coupling bandwidths can be modified for each resonator chamber of a filter chamber and thereby for each resonator in a filter chamber by modifying the diameter of at least one resonator chamber of a filter chamber, which is possible, by way of example, by exchanging the at least one insert for another insert with a modified size. The arrangement and/or the number and/or the size and/or the cross-section shape of the at least one coupling opening can also be modified by turning and/or exchanging the at least one separator. Likewise, the resonance frequency and/or the coupling bandwidth can be modified by rotating inward or outward at least one tuning element into/out of at least one resonator chamber of a filter chamber. Finally, the dielectric in a filter chamber can be exchanged for another dielectric with modified dimensions and/or recesses.
Various non-limiting embodiments are described in detail below as examples with reference to the drawings. Objects which are the same have the same reference numbers. In the corresponding figures of the drawings,